Lying facedown (5)
I believe the answer is:
prone
'lying facedown' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for prone that I've seen before include "Recumbent, likely" , "Lying face downward" , "Placed face down" , "Liable (to suffer) - lying down" , "Lying face down - inclined" .)